1. Field of the Invention
The invention lies within the area of materials-handling technology. It relates to a gripper for grasping objects and conveying held objects, in particular spatially extended, symmetrical objects, objects with a retaining ring, hollow objects, objects with different forms and/or sizes. The gripper is suited in particular for grasping and conveying preforms for the production of vessels made of plastics material, for example PET bottles. The invention also relates to a conveyor system having such grippers and to a method for operating such a conveyor system.
2. Description of Related Art
In materials-handling technology, there is a need for grippers which are simple and cost-efficient to produce, are sturdy and flexible to use and are able to grasp and convey objects of different forms and quality in a reliable manner.
For example, grippers are used in order to convey preforms for the blow-molding of containers made of plastics material and to convey the produced containers between different stations of the blow-molding system. The preforms are hollow bodies which are made of a thermoplastic plastics material, are open on the one side and have a substantially rotationally-symmetrical form. As a rule, they have a thread and a retaining ring. Known grippers for preforms are developed in the manner of tongs. The gripper jaws are arranged in one plane which lies at right angles with respect to the rotational axis of the preform. They engage under the retaining ring in the manner of a fork by approaching from the side. Conveying apparatuses having such grippers consequently need a relatively large amount of space in the receiving region. In the region in which they grasp the object (clamping region) the gripper jaws are concave in form and are consequently adapted to the cylindrical form below the retaining ring. In this way, objects with different diameters are able to be grasped, however, only within certain maximum and minimum diameters. Examples of known preform grippers are described in US 2010/0278959, U.S. Pat. No. 6,612,634 or DE 10325693. Clamping mandrels which can be inserted into a mouth region of the preform for retention are used as an alternative to this.
U.S. Pat. No. 4,921,294 makes known a gripper for grasping flat products, in particular printed products, said gripper including a gripper body and a fixed and a movable gripper jaw. The design is mirror-symmetrical. The movable gripper jaw is formed by a mirror-symmetrical wire bow made of spring steel. The wire bow is formed in its end region in each case to form a helix. In addition, proceeding from the helices, it forms two holding tongues. These are oriented at right angles to the axis of the helices and are spaced apart from one another. Between the holding tongues the bow is curved such that it forms an elongated, straight bow part which is situated in the vicinity of the common axis of the helices and acts as a pressing element. The helices are placed onto journals which are arranged on opposite sides of the gripper body and coincide with one another. By the helices being fixed in the gripper body, the wire bow is prestressed against the fixed gripper jaw. The journal defines a pivot axis about which the gripper jaw is able to rotate. The gripper jaw is actuated by two control elements which press in each case onto the wire bow in the region of the holding tongue. Said control elements press the movable gripper jaw away from the fixed gripper jaw when they are actuated together. They are prestressed against the movable gripper jaw for this purpose.
Said design is adapted to flat objects as a result of the forming of the bow with two protruding tongues and one elongated pressing element. It is not suitable for conveying spatially extended objects with different forms. The actuating mechanism consists of several parts and is consequently expensive to produce and maintain.